International Standard Book Number
The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay.
The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces.
Separating the parts of a 10-digit ISBN is done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
International Commission on Illumination
The International Commission on Illumination is the international authority on light, illumination and colour spaces. It was established in 1913 as a successor to the Commission Internationale de Photométrie and is based in Vienna. The President from 2015 is Yoshihiro Ohno from the US, in 1976, the commission developed the CIELAB and CIELUV colour spaces, which are widely used today. Based on CIELAB, colour difference formulas CIEDE94 and CIEDE2000 were recommended in the corresponding years
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.
Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays and radio waves are light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400.
Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body. It has a spectrum and intensity that depends only on the bodys temperature. The thermal radiation emitted by many ordinary objects can be approximated as black-body radiation. A black-body at room temperature appears black, as most of the energy it radiates is infra-red, when it becomes a little hotter, it appears dull red. As its temperature increases further it eventually becomes blue-white, although planets and stars are neither in thermal equilibrium with their surroundings nor perfect black bodies, black-body radiation is used as a first approximation for the energy they emit. Black holes are near-perfect black bodies, in the sense that they absorb all the radiation that falls on them and it has been proposed that they emit black-body radiation, with a temperature that depends on the mass of the black hole. The term black body was introduced by Gustav Kirchhoff in 1860, Black-body radiation is called thermal radiation, cavity radiation, complete radiation or temperature radiation.
Black-body radiation has a characteristic, continuous spectrum that depends only on the bodys temperature. As the temperature increases past about 500 degrees Celsius, black start to emit significant amounts of visible light. Viewed in the dark by the eye, the first faint glow appears as a ghostly grey. When the body appears white, it is emitting a substantial fraction of its energy as ultraviolet radiation, Black-body radiation provides insight into the thermodynamic equilibrium state of cavity radiation. Instead, in theory the occupation numbers of the modes are quantized, cutting off the spectrum at high frequency in agreement with experimental observation. The study of the laws of black bodies and the failure of classical physics to describe them helped establish the foundations of quantum mechanics, all normal matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a thermal energy into electromagnetic energy. It is a process of radiative distribution of entropy.
Conversely all normal matter absorbs electromagnetic radiation to some degree, an object that absorbs all radiation falling on it, at all wavelengths, is called a black body. When a black body is at a temperature, its emission has a characteristic frequency distribution that depends on the temperature. Its emission is called black-body radiation, the concept of the black body is an idealization, as perfect black bodies do not exist in nature
Passive infrared sensor
A passive infrared sensor is an electronic sensor that measures infrared light radiating from objects in its field of view. They are most often used in PIR-based motion detectors, all objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation isnt visible to the eye because it radiates at infrared wavelengths. The term passive in this instance refers to the fact that PIR devices do not generate or radiate any energy for detection purposes and they work entirely by detecting the energy given off by other objects. PIR sensors dont detect or measure heat, instead they detect the radiation emitted or reflected from an object. Infrared radiation enters through the front of the sensor, known as the sensor face, at the core of a PIR sensor is a solid state sensor or set of sensors, made from pyroelectric materials—materials which generate energy when exposed to heat. Typically, the sensors are approximately 1/4 inch square, and take the form of a thin film, materials commonly used in PIR sensors include gallium nitride, caesium nitrate, polyvinyl fluorides, derivatives of phenylpyridine, and cobalt phthalocyanine.
The sensor is often manufactured as part of an integrated circuit, a PIR-based motion detector is used to sense movement of people, animals, or other objects. They are commonly used in burglar alarms and automatically-activated lighting systems and they are commonly called simply PIR, or sometimes PID, for passive infrared detector. The sensor converts the resulting change in the infrared radiation into a change in the output voltage. PIRs come in many configurations for a variety of applications. The most common models have numerous Fresnel lenses or mirror segments, a range of about ten meters. Models with wider fields of view, including 360 degrees, are designed to mount on a ceiling. Some larger PIRs are made with single segment mirrors and can sense changes in infrared energy over thirty meters away from the PIR. There are PIRs designed with reversible orientation mirrors which allow either broad coverage or very narrow curtain coverage, pairs of sensor elements may be wired as opposite inputs to a differential amplifier.
This allows the device to resist false indications of change in the event of being exposed to brief flashes of light or field-wide illumination, at the same time, this differential arrangement minimizes common-mode interference, allowing the device to resist triggering due to nearby electric fields. However, a pair of sensors cannot measure temperature in this configuration. The PIR sensor is mounted on a printed circuit board containing the necessary electronics required to interpret the signals from the sensor itself
Messier 82 is a starburst galaxy about 12 million light-years away in the constellation Ursa Major. A member of the M81 Group, it is five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxys center. The starburst activity is thought to have triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to Earth, M82 is the example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014, in 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2. M82 was previously believed to be an irregular galaxy, in 2005, two symmetric spiral arms were discovered in near-infrared images of M82. The arms were detected by subtracting an axisymmetric exponential disk from the NIR images, even though the arms were detected in NIR images, they are bluer than the disk. The arms were previously missed due to M82s high disk surface brightness, the nearly edge-on view of this galaxy and these arms emanate from the ends of the NIR bar and can be followed for the length of 3 disc scales.
Assuming that the part of M82 is nearer to us, as most of the literature does. In 2005, the Hubble Space Telescope revealed 197 young massive clusters in the starburst core, the average mass of these clusters is around 200,000 solar masses, hence the starburst core is a very energetic and high-density environment. Throughout the galaxys center, young stars are being born 10 times faster than they are inside the entire Milky Way Galaxy, in the core of M82, the active starburst region spans a diameter of 500 pc. Four high surface brightness regions or clumps are detectable in this region at visible wavelengths and these clumps correspond to known sources at X-ray and radio frequencies. Consequently, they are thought to be the least obscured starburst clusters from our vantage point. M82s unique bipolar outflow appears to be concentrated on clumps A and C and is fueled by energy released by supernovae within the clumps which occur at a rate of one every ten years. The Chandra X-ray Observatory detected fluctuating X-ray emissions from a location approximately 600 light-years away from the center of M82, astronomers have postulated that this fluctuating emission comes from the first known intermediate-mass black hole, of roughly 200 to 5000 solar masses. M82, like most galaxies, hosts a supermassive black hole at its center with a mass of approximately 3 x 107 solar masses as measured from stellar dynamics, there have been several theories about the nature of this object, but currently no theory entirely fits the observed data.
However, all known microquasars produce large quantities of X-rays, whereas the objects X-ray flux is below the measurement threshold, the object is located at several arcseconds from the center of M82 which makes it unlikely to be associated with a supermassive black hole. It has an apparent superluminal motion of four times the speed of light relative to the galaxy center, apparent superluminal motion is consistent with relativistic jets in massive black holes and does not indicate that the source itself is moving above lightspeed
In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space carrying electromagnetic radiant energy. It includes radio waves, infrared, ultraviolet, X-, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to other and perpendicular to the direction of energy and wave propagation. The wavefront of electromagnetic waves emitted from a point source is a sphere, the position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can interact with other charged particles. EM waves carry energy and angular momentum away from their source particle, quanta of EM waves are called photons, whose rest mass is zero, but whose energy, or equivalent total mass, is not zero so they are still affected by gravity.
Thus, EMR is sometimes referred to as the far field, in this language, the near field refers to EM fields near the charges and current that directly produced them, electromagnetic induction and electrostatic induction phenomena. In the quantum theory of electromagnetism, EMR consists of photons, quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of a photon is quantized and is greater for photons of higher frequency. This relationship is given by Plancks equation E = hν, where E is the energy per photon, ν is the frequency of the photon, a single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light. The effects of EMR upon chemical compounds and biological organisms depend both upon the power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, the effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons.
In contrast, high ultraviolet, X-rays and gamma rays are called ionizing radiation since individual photons of high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the speed of light. Maxwell’s equations were confirmed by Heinrich Hertz through experiments with radio waves, according to Maxwells equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the field are always accompanied by a wave in the magnetic field in one direction
An infrared heater or heat lamp is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the body, the wavelength of the peak of the infrared radiation ranges from 780 nm to 1 mm. No contact or medium between the two bodies is needed for the energy transfer, infrared heaters can be operated in vacuum or atmosphere. One classification of infrared heaters is by the bands of infrared emission. German-British astronomer Sir William Herschel is credited with the discovery of infrared in 1800 and he made an instrument called a spectrometer to measure the magnitude of radiant power at different wavelengths. This instrument was made from three pieces, through his experiment Herschel found that red light had the highest degree of temperature change in the light spectrum, infrared heating was not commonly used until World War II. During World War II infrared heating became more used and recognized. The main applications were in the metal finishing fields, particularly in the curing and drying of paints, banks of lamp bulbs were used very successfully but by todays standards, the power intensities were very low.
The technique offered much faster drying times than the fuel convection ovens of the time, production bottlenecks were mitigated and military supplies to the armed forces were maintained. After World War II the adoption of infrared heating techniques continued, in the mid 1950s the motor vehicle industry began to show interest in the capabilities of infrared for paint curing and a number of production line infrared tunnels came into use. The most common filament material used for infrared heaters is tungsten wire. Low temperature alternatives for tungsten are carbon, or alloys of iron, while carbon filaments are more fickle to produce, they heat up much more quickly than a comparable medium-wave heater based on a FeCrAl filament. When light is undesirable or not necessary in a heater, ceramic infrared radiant heaters are the preferred choice, containing 8 meters of coiled alloy resistance wire, they emit a uniformed heat across the entire surface of the heater and the ceramic is 90% absorbent of the radiation.
As absorption and emission are based on the physical causes in each body. Industrial infrared heaters sometimes use a coating on the quartz tube that reflects the infrared radiation. Consequently, the infrared radiation impinging on the product is virtually doubled, gold is used because of its oxidation resistance and very high IR reflectivity of approximately 95%. Infrared heaters are used in infrared modules combining several heaters to achieve larger heated areas. Their peak wavelength is well below the absorption spectrum for water and they are well suited for heating of silica where a deep penetration is needed
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can be applied to periodic waves of non-sinusoidal shape. The term wavelength is applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height.
The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively.
Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
It extends from the nominal red edge of the visible spectrum at 700 nanometers, to 1000000 nm. Most of the radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon, slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an effect on Earths climate. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements and it excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range, Infrared radiation is used in industrial and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected, Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatuses.
Thermal-infrared imaging is used extensively for military and civilian purposes, military applications include target acquisition, night vision and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm, Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm. This range of wavelengths corresponds to a range of approximately 430 THz down to 300 GHz. Below infrared is the portion of the electromagnetic spectrum. Sunlight, at a temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level, of this energy,527 watts is infrared radiation,445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight.
Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, thermal infrared radiation has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wiens displacement law. Therefore, the band is often subdivided into smaller sections. Due to the nature of the blackbody radiation curves, typical hot objects, such as exhaust pipes, the three regions are used for observation of different temperature ranges, and hence different environments in space
The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels.
Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch.
Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
Wien's displacement law
Wiens displacement law states that the black body radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature. The shift of that peak is a consequence of the Planck radiation law which describes the spectral brightness of black body radiation as a function of wavelength at any given temperature. B is a constant of proportionality called Wiens displacement constant, equal to 2. 8977729×10−3 m⋅K, or more conveniently to obtain wavelength in micrometers, b ≈2900 μm·K. If one is considering the peak of black body emission per unit frequency or per proportional bandwidth, however the form of the law remains the same, the peak wavelength is inversely proportional to temperature. Wiens displacement law may be referred to as Wiens law, a term which is used for the Wien approximation. One easily observes changes in the color of an incandescent light bulb as the temperature of its filament is varied by a light dimmer. As the light is dimmed and the filament temperature decreases, the distribution of color shifts toward longer wavelengths and the light appears redder, as well as dimmer.
It is easy to calculate that a fire at 1500 K puts out peak radiation at about 2000 nm. 98% of its radiation is beyond 1000 nm. Consequently, a campfire can keep one warm but is a source of visible light. The effective temperature of the Sun is 5778 K, using Wiens law, one finds a peak emission per nanometer at a wavelength of about 500 nm in the green portion of the spectrum near the peak sensitivity of the human eye. On the other hand, in terms of power per unit optical frequency, in terms of power per percentage bandwidth, the peak is at about 635 nm, a red wavelength. Regardless of how one wants to plot the spectrum, about half of the radiation is at wavelengths shorter than 710 nm. Of that, about 12% is at wavelengths shorter than 400 nm and it can be appreciated that a rather large amount of the Suns radiation falls in the fairly small visible spectrum. The preponderance of emission in the range, however, is not the case in most stars. The hot supergiant Rigel emits 60% of its light in the ultraviolet, with both stars prominent in the constellation of Orion, one can easily appreciate the color difference between the blue-white Rigel and the red Betelgeuse.
While few stars are as hot as Rigel, stars cooler than the sun or even as cool as Betelgeuse are very commonplace, mammals with a skin temperature of about 300 K emit peak radiation at around 10 μm in the far infrared. This is therefore the range of infrared wavelengths that pit viper snakes, when comparing the apparent color of lighting sources, it is customary to cite the color temperature. Note that the description of the former color as cool